1 Plate Tectonics and Climate 陳奕穎 Chapter 5 of EARTH’S CLIMATE Institute of Hydrological Sciences

2 Plate tectonic process Glaciation alternation Climate model Changes CO 2 IcehouseGreenhouse Ex: 200Myr ago Two hypotheses Polar Position Hypothesis BLAG Spreading RateUplift Weathering

Institute of Hydrological Sciences 3 Plate tectonics: The scientific theory which describe Earth is called plate tectonics.  Wegener[1914] find the margins of eastern South America and western Africa, could fit together.

Institute of Hydrological Sciences 4 Structure and Composition of Tectonic Plates Earth Outer Layers chemical composition  Continental crust (30-70 km) Granites ( 花崗岩 ) 2.7 g/cm 3  Ocean crust (5-10 km) Basalts ( 玄武岩 ) 3.2 g/cm 3  Mantle (Fe, Mg) to 2890 km >3.6 g/cm 3 Physical behavior  Lithosphere (100 km) hard, rigid unit that forms the tectonic plates  Asthenosphere ( km) softer unit capable of flowing

Institute of Hydrological Sciences 5 Tectonic plates  The outer rigid layer of Earth is broken into about dozen major segments called plates.

Institute of Hydrological Sciences 6 Plate boundaries  Divergent margins  Convergent margins  Transform fault margins

Institute of Hydrological Sciences 7 Evidence of past plate motions  Earth magnetic field  evidence of Plate tectonics rearranging Earth’s geography  Energy from the magnetic field which result from molten fluids circulating in Earth’s liquid iron core.

Institute of Hydrological Sciences 8 Magnetic lineations  Molten fluid record magnetic field.

Institute of Hydrological Sciences 9 Paleomagnetic determination of past location of continents  Basalt is the best rocks to use (rich in highly magnetic iron).  No ocean crust older than 175 Myrs.  For earlier interval, it must focus on basalts on the continent.  500Myrs less reliable because of increasing likelihood that their magnetic signatures have been rest to the magnetic field of a later time.

Institute of Hydrological Sciences 10 Short Summery  We can reconstruct the position of the continents with good accuracy back to 300 Myrs ago.  To measure rates of the seafloor spreading in ocean basin.  Even we can compile spreading rates over enough of the world’s ocean to estimate the global mean rate of creation and destruction of ocean crust.

Institute of Hydrological Sciences 11 The Polar Position Hypothesis :  ice sheets should appear on continents when they located at polar or near-polar latitude,  but no ice should appear anywhere on Earth if no continent exist anywhere near poles.

Institute of Hydrological Sciences 12 Moving continents

Institute of Hydrological Sciences 13 Laurasia Gondwana Pengaea  Laurasia: North-central Asia, Europe, North American  Gondwana: Africa, Arabia, Antarctica, Australia, South America, and India.

Institute of Hydrological Sciences 14 Gondwana and South Pole

Institute of Hydrological Sciences 15 Glaciations and Continental Positions since 500 Myr Ago Why ? CO 2 IcehouseGreenhouse

Institute of Hydrological Sciences 16 Modeling Climate on the Supercontinent Pangaea  Climate scientist use general circulation models (GCMs) to evaluate the impact of geography as well as several other factors. Questions: What level of atmospheric CO 2 ? Dose it match geologic record ?

Institute of Hydrological Sciences 17 Input to the Model Simulation of Pangaean Climate  Boundary condiction: Distribution of land and sea Global sea level Using simplified symmetrical Comparable to today’s 200 Myr ago Topography 1000 m

Institute of Hydrological Sciences 18 Input to the Model Simulation of Pangaean Climate cont. 4.Climate modelers constrain the likely CO 2 level in atmosphere. 5.Astrophysical modelers indicate Sun’s energy weaker 1% than today’s.

Institute of Hydrological Sciences 19 Output from the Model Simulation of Pangaean Climate  Dry continental climate 1.the great expanses of land at subtropical latitudes beneath the dry. 2.trade wind lose most of their water vapor by the time they reached the continental interior Uplift Downward

Institute of Hydrological Sciences 20 Output from the Model Simulation of Pangaean Climate cont.  Monsoon circulations Different rates of response of the land and sea to heating in summer and radiative heat loss in winter

Institute of Hydrological Sciences 21 Tectonic Control of CO 2 Input  BLAG[1983] (the geochemists Robert Berner, Antonio Lasaga, Robert Garrels) Climate changes during the last several hundred million years have been driven mainly by changes in the rate of CO 2 into the atmosphere by plate tectonic process.(spreading rate hypothesis) Spreading ratesClimate change CO 2 Change

Institute of Hydrological Sciences 22 Age of the seafloor  Spreading rates are as much as ten times faster in the Pacific than in Atlantic.

Institute of Hydrological Sciences 23 Earth’s Negative Feedback

Institute of Hydrological Sciences 24 Tectonic-scale Carbon cycle Silicate rockAtmospherePlankton Ocean sedimentSilicate rockAtmosphere Imbalance CO 2 Climate changes

Institute of Hydrological Sciences 25 A Warmer Earth 100Myr Ago  The global mean spreading rate was as much as 50% faster 100Myr ago than it is at present, so the rate of input of CO 2 from the rocks to atmosphere must be higher than today.

Institute of Hydrological Sciences 26 The Uplift Weathering Hypothesis Chemical weathering Rock exposure Fresh rock Exposure time

Institute of Hydrological Sciences 27 Fragmentation of Rock Weathering and Exposure Time

Institute of Hydrological Sciences 28 Three Hypotheses:

Institute of Hydrological Sciences 29 Conclusions:  Plate tectonic process largely explains alternations between icehouse intervals.  Atmospheric CO 2 changes in tectonic-scale in the last hundred million years needed to explain the climate variability.  Both spreading rate & uplift hypotheses attempt to link the changes in CO 2 and in plate tectonic.